In a large-current semiconductor device, a semiconductor element is a heating body and thus generates a large amount of heat during use. Therefore, the configuration that heat sink or dissipating plates are joined respectively to both surfaces of a semiconductor element has been proposed to improve heat dissipation property. FIG. 15 is a sectional view of a conventional semiconductor device provided with heat dissipating plates on both surfaces of a semiconductor element. A semiconductor device 100 is configured such that a semiconductor element 101 is held between a first electrode 102 and a second electrode 103 and further a block electrode 104 is placed between the semiconductor element 101 and the first electrode 102. The semiconductor element 101, first electrode 102, second electrode 103, and block electrode 104 which are laid one on another are respectively joined to one another through solder, thus forming solder layers 105.
The first electrode 102 and second electrode 103 are placed as an emitter electrode and a collector electrode which are main electrodes of the semiconductor element 101 and also function as heat dissipating plates. Those electrodes 102 and 103 are therefore made of metal providing good electric conductivity and heat conductivity, such as copper and aluminum. The block electrode 104 is similarly made of metal providing good electric conductivity and heat conductivity, such as copper and aluminum. Those first electrode 102 and second electrode 103 are connected respectively to main electrode terminals not shown. A control electrode terminal 111 is connected to the semiconductor element 101 through a bonding wire 112. Those components are wholly molded with resin 108.